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Tello PCB and antenna reference, to help fellow crazy modders ;)

ph2t

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I've been working on a few mods that have required me to gut my poor tello several times over. I have put together a couple of pictures that have helped me with my modding. Motor and antenna pinouts, etc.

I'm doing some more research into the tello antenna configuration and will post on that here as well. Write-ups take time, especially when you want to lay a lot of information out in a way that helps others. Please be patient with me as I add my thoughts and results to this thread. ;)

Tello printed circuit board (PCB) layout - viewed from the underside.

PCB pinout.jpg
Notes on the above picture:
  • The antenna is approx. 10mm in length, at 2.4GHz this puts it at less 1/10th of the wavelength of the Wi-Fi signal. An antennas length is guided by wavelength of the signal it is carrying. Wavelength is to do with frequency. I won't go into it here, google "wavelength and antennas" to get the gist. The diagram above quotes 1/4 wavelength, this is incorrect.

Tello antenna PCB - located in the two rear motor mounts.
tello antenna.jpg


Notes on the above picture:
  • The tello has two independent antennas that are not directly connected
    • According to other forum posts here it is a smart antenna array (two antennas located in each rear motor mount) that dynamically changes between each antenna depending on which one has the better signal connection to the smartphone controlling it.
    • The antennas are patch antennas, a flat antenna that is etched onto a PCB. Usually the ground plane is located on the other side of the PCB - in case of the tello the circular coil located above the antenna is the ground plane.
  • The antenna is approx. 10mm in length, at 2.4GHz this puts it at less 1/10th of the wavelength of the Wi-Fi signal. An antennas length is guided by wavelength of the signal it is carrying. Wavelength is to do with frequency. I won't go into it here, google "wavelength and antennas" to get the gist.
  • Antennas under a 1/2 wavelength generally perform better when provided with a ground plane (old engineering degree notes here, I might be wrong). The coil shaped wire in the above picture is providing the ground plane for the small antenna that is on the PCB.
  • All the transmitting and receiving for the tello is done through its two rear feet, not the arms nor the chassis.

More to come... Just getting this up for the moment and I'll edit/contribute more as a test and confirm my theories.
cheers,
ph2t.
 
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Customerx

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Excellent work, looking forward to this mod. :)
 

raulvolador

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@ph2t, an awesome job :)

I have learned a lot about tello inside looking at your diagrams.

Thank a lot, and keep us informed.

raul.
 
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Customerx

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Vollatello, love your app. Haven't had a full play with it outside as yet but love what I'm seeing. :)
 
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umanbean

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I have put together a couple of pictures that have helped me with my modding. Motor and antenna pinouts, etc.
Thank you for the well-labelled photos, very nice. I'll likely never mod my antennas but I love learning and you did a good job of explaining
 

Flydrone

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really very interesting, congratulations for this your study on tello antennas.(y)
 

Garana

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I've been working on a few mods that have required me to gut my poor tello several times over. I have put together a couple of pictures that have helped me with my modding. Motor and antenna pinouts, etc.

I'm doing some more research into the tello antenna configuration and will post on that here as well. Write-ups take time, especially when you want to lay a lot of information out in a way that helps others. Please be patient with me as I add my thoughts and results to this thread. ;)

Tello printed circuit board (PCB) layout - viewed from the underside.

View attachment 2605
Notes on the above picture:
  • The antenna is approx. 10mm in length, at 2.4GHz this puts it at less 1/10th of the wavelength of the Wi-Fi signal. An antennas length is guided by wavelength of the signal it is carrying. Wavelength is to do with frequency. I won't go into it here, google "wavelength and antennas" to get the gist. The diagram above quotes 1/4 wavelength, this is incorrect.

Tello antenna PCB - located in the two rear motor mounts.
View attachment 2606


Notes on the above picture:
  • The tello has two independent antennas that are not directly connected
    • According to other forum posts here it is a smart antenna array (two antennas located in each rear motor mount) that dynamically changes between each antenna depending on which one has the better signal connection to the smartphone controlling it.
    • The antennas are patch antennas, a flat antenna that is etched onto a PCB. Usually the ground plane is located on the other side of the PCB - in case of the tello the circular coil located above the antenna is the ground plane.
  • The antenna is approx. 10mm in length, at 2.4GHz this puts it at less 1/10th of the wavelength of the Wi-Fi signal. An antennas length is guided by wavelength of the signal it is carrying. Wavelength is to do with frequency. I won't go into it here, google "wavelength and antennas" to get the gist.
  • Antennas under a 1/2 wavelength generally perform better when provided with a ground plane (old engineering degree notes here, I might be wrong). The coil shaped wire in the above picture is providing the ground plane for the small antenna that is on the PCB.
  • All the transmitting and receiving for the tello is done through its two rear feet, not the arms nor the chassis.

More to come... Just getting this up for the moment and I'll edit/contribute more as a test and confirm my theories.
cheers,
ph2t.
That's so great. Thank's for sharing.
 

Customerx

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Had a thought, I used to play around with arduinos. Have been looking at the esp8266 chip. Apparently has a range of 300 - 500 m, placing on top of the tello with a reasonably larger
antenna and using as a WiFi repeater could extend the range. Without playing with the tello internals.

So it would go.... Tello to esp8266
Fastened to the tello, new housing for top cover and also powered by tello battery)
Esp8266 as a repeater capable of 5mbps,

then to mi xaomi to phone.

Wonder what the lag would be, maybe add an sdcard for video if can pull out the data, should be able to as it streams. Maybe even add GPS.

Any ideas, anyone done anything similar?
 
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raulvolador

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Had a thought, I used to play around with arduinos. Have been looking at the esp8266 chip. Apparently has a range of 300 - 500 m, placing on top of the tello with a reasonably larger
antenna and using as a WiFi repeater could extend the range. Without playing with the tello internals.

So it would go.... Tello to esp8266
Fastened to the tello, new housing for top cover and also powered by tello battery)
Esp8266 as a repeater capable of 5mbps,

then to mi xaomi to phone.

Wonder what the lag would be, maybe add an sdcard for video if can pull out the data, should be able to as it streams. Maybe even add GPS.

Any ideas, anyone done anything similar?
Some weeks ago I bought an ESP8266 WIFI chip ESP8266 - Wikipedia

I can confirm it's a very interesting low-cost investment.

In my case, I am trying to use it to get Tello choosing WIFI channel that I want.

Tello WIFI channel selection

My plan is writing a little script for flooding neighbour WIFI channels with fake data, letting free only the channel I want Tello use for comunications. Once Tello make its channel decission I'll swithc off ESP8266 for no WIFI disturbance.

That's my idea. I´ll keep you informed

All the best.
 

Customerx

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There are some pre loaded boards on eBay that block WiFi, so the script would probably be on GitHub,
Tello priority app lol (can't see anyone having any problems with this idea oooops ;)
Found this tho.



Also thought about the esp32 yet there doesn't seem to be as much versatility as yet with this chip. Like the adafruit huzzah tho, looks easy to set up, especially with the SD card stacking option.
 

raulvolador

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You are right.

In fact, I bought a pre-loaded board from ESP8266 Deauther 2.0 GitHub proyect. You can read more about project here:

spacehuhn/esp8266_deauther

Script I am writing uses this set of commands:

spacehuhn/esp8266_deauther

send beacon <mac> <ssid> <ch> [wpa2]

Sends single packet out with giving parameters.

You can also sent out custom packets with: send packet <packet>
The packet must be a hexadecimal string devided by : and with a leading zero.
It's only recommended to use this feature if you have experience on how the ESP8266 handles sending custom defined packets.
All the best.

deauther.jpg
 

Customerx

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As long as we are responsible and dont use this as a frequency jammer for selfish reasons tho, wouldn't condone the illegal use but as a quick kick n fix to prioritise a channel for your own use is surely acceptable.
Just a Quick disclaimer as I like this forum ;)
 

Customerx

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Oh and the esp32 has some range!! Just in case it is possible to use as a repeater, there will be some script somewhere.

 

ph2t

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Great stuff guys, way to hijack a thread! haha, just kidding! I hope the work with the esp32 chip pays off some benefits.

I have been doing some more work on the subject of antennas, all the efforts everyone is going to has really impressed me with the different antenna styles.

I think in the end what antenna style works depends on your flying patterns. I've noticed that flying around 12 - 17m altitude gives me the best reception. There are many factors at play here. The antenna mod I have done is a bit nasty, combining the two antennas etc is not the best. Without the physical separation neither antenna can offer a different coverage area or alignment of signal.

Here is an epic FPV flight I did around work yesterday. Wind was moderate to light and I was in fast mode for the whole time. The video is jumpy (I'm flying in fast mode) and prolyl not that interesting but it does show some things about reception and the antennas. Fly too high and lose signal because I don't have the antennas positioned in the stock tello location of under the feel, vertically polarised. This helps with reception when the RX is higher than the TX.


  • Massive flight time - 10mins 36 seconds, all in fast mode and hammering along pretty hard on the throttle with the racerstar motors.
  • Flying over large buildings (that contain approx. 50 wifi access points across the whole area - school wifi network) with all sorts of interference going on.
  • I loose video signal a few times, used a spotter to help when I lost fpv signal.
  • Was forced by the tello to land, twice! (successfully cancelled the operation and kept flying). Dunno why this occurred, I think the VPS had a cow one to many times and got sick of my flying style, lol.
  • Survived a low battery notification on my phone that put the tello app to the back ground whilst coming into a dive run.

I'm going to try a combination of directional and omni-direction antennas on the wifi repeater.

One antenna will stay as it is and the other will be replaced with this directional:
directional_ant.png
I will point this directional at the buildings. See how it goes.

On the tello I was thinking of making some whip style antennas, using the information here as a guide.
repair-2-4ghz-antenna-rx - some points around antenna length and shielded coz length are interesting.

One antenna would be sticking up vertically out of the top of the tello. Here is a top view.
vert_p_antenna.jpg

One antenna would be aligned along the bottom of the tello, horizontally.
horiz_p_antenna.jpg

My thoughts are this would help with flying, give good separation between antennas and offer both horizontal and vertically polarized signal variations. The tello would then select which antenna is providing the best signal strength. This is my theory.

I will perform another video like the one above using my stock tello when I get a better day to fly. I want to see how much of an impact the stock antenna placement has on signal.

cheers,
ph2t.
 

Stele

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Great flight. Can't wait to see your results with the new antenna setup on the repeater and the tello.
One note regarding your plans about the horizontal antenna under the tello.
Guiding the antenna directly by the FC and all its HF-Noise is something you want to avoid. Perhaps better stick it out the back.


Time for a modding sub-forum!

Regards Stele
 
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mcsound

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Respect for this initiative!
I don't understand much in atennas, but what if you install another two antennas inside the front legs of Tello similar to what are already installed in rear ones? Or even make bigger legs with more powerful antennas? That will save the overall sleek look of the drone without any protruding frankenparts + save the balance and aerodynamics...
Just my 2 cents. :)
 

iHello

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Thanks ph2t! Very detailed and informative post. Can you tell me how to remove the rubber part of the leg? I need to solder back the wire that came off the antenna after a crash.
 

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